The results show that, over time, more people who use e-cigarettes start smoking than people who do not use e-cigarettes. The SBU concludes that the quality of evidence is moderate, which means that it is likely that there is an association. However, according to the conclusions, it is not possible to determine how strong the association is, and the causes of the differences between the groups are unclear.
Similar results can also be seen in people who use snus. Over time, more people using snus start to smoke than people who do not use snus. However, the SBU concludes that the quality of evidence of these results is low, as material for studying the use of snus is limited. This means that it is possible that there is an association but that it is not possible to draw any firm conclusions.
The SBU has also investigated whether the use of e-cigarettes or snus can lead to a change in the smoking habits of those who already smoke. Here, however, the scientific evidence is too uncertain for any conclusions to be drawn on changes in smoking habits. This applies to all types of change – both stopping smoking and increased or reduced smoking of tobacco.
About the systematic review
The SBU conducted the systematic review in agreement with the Public Health Agency of Sweden. It is based on a review of studies in accordance with the SBU’s methods for systematic literature overviews.
The literature searches examined scientific databases for studies published up to November 2019. In total, 73 studies met the inclusion criteria of the review. Of these, 65 studies examined the associations between using e-cigarettes and using smoking tobacco. Eight studies considered the associations between using snus and using smoking tobacco. The results from the individual studies were combined in meta-analyses, and were also analysed separately in respect of men and women, young people under 18 and adults. The reliability of the results was then assessed using the GRADE system.
Conflicts of interest
The SBU has assessed whether there are any conflicts of interest relating to the studies included in the results. Separate supplementary analyses were carried out where required on material that excluded studies linked to companies producing or selling e-cigarettes, snus or smoking tobacco. This summary reports only on the results from studies without any such links.
Link to the SBU’s website and the report (sbu.se)(in Swedish)
In what ways are the results from the SBU’s systematic review significant?
The results highlight in particular how tobacco smoking amongst the population can be affected when new types of products become more available; for example, e-cigarettes, which can increase the likelihood of someone starting to smoke.
The link between using e-cigarettes and starting to smoke is more reliable in the case of people under 18, which emphasises the importance of protecting children and young people in tobacco prevention work.
The results should also be seen as part of the body of knowledge underpinning tobacco prevention work, for example, knowledge about health risks, prevalence of use and which groups are affected, and the various factors that affect equitable health.
Find out more about tobacco prevention work (in Swedish)
What are the boundaries of the systematic review?
The systematic review does not address health risks but focuses on how habits and behaviour are affected when different tobacco and nicotine products are used by the population.
Neither does it evaluate the impact of e-cigarettes and snus as products that can help people stop smoking. E-cigarettes and snus are neither approved nor recommended as smoking cessation products in Sweden. There are other effective and safe methods to help people stop smoking.
Find out more on the National Board of Health and Welfare’s website (socialstyrelsen.se) (in Swedish)
Are the results transferable to Swedish circumstances?
The studies on e-cigarettes included in the results were carried out in many different countries, mainly in the United States. To date, there have been no studies published from the Nordic countries. This makes it rather difficult to assess the transferability of the results to Swedish circumstances, as several factors come into play. For example, product availability and legislation may not be the same in other countries as in Sweden. Transferability can also be affected by cultural differences.
The studies on snus were carried out in Norway, Sweden and Finland. However, transferring the results to the general population is not straightforward as some of the results are based on studies involving only boys.
How will the Public Health Agency of Sweden use the results?
We plan to make the results available to relevant target groups in tobacco prevention work. For example, the Act on Tobacco and Similar Products is currently being overhauled, and includes a review of the regulation of e-cigarettes.
Why does the Public Health Agency of Sweden only use results from independent research?
Our work in tobacco prevention is based on the WHO Framework Convention on Tobacco Control. Article 5.3 states that “Parties shall act to protect these policies from commercial and other vested interests of the tobacco industry”. According to the Framework Convention, there is a fundamental, unresolvable conflict between the interests of the tobacco industry and public health policy interests, and so we only use results from research that has no links to commercial or other interests in the tobacco industry.